Question

Why does temperature remain constant as a liquid is heated and gets converted to its gaseous state at its boiling point?
(A) Due to increase in potential energy
(B) Due to increase in kinetic energy
(C) due to decrease in potential energy
(D) Due to decrease in kinetic energy

Answer 1

The boiling point of a substance is the temperature at which the vapour pressure of a liquid is equal to the pressure of the surrounding of the liquid and then the liquid changes into vapour thus, we can say that the boiling point of a liquid varies as depending upon the surroundings of the environment.

Complete step by step answer:
The process by which a liquid is turned into vapours when it is exposed to heat is called boiling. Also in this process, it is mandatory to heat the liquid up to its boiling point. When the vapour pressure of the liquid becomes equal to the atmospheric pressure exerted above the liquid. Then we can say that the liquid phase has been changed to its gaseous phase.
The different liquids have different boiling points and they boil at this specific temperature only. At first when the temperature starts to rise, then the liquid does take its time to maintain the temperature in the whole liquid. Thus when the temperature of the whole liquid becomes uniform, only then the further increase in the temperature would occur. This process will continue until the temperature of the liquid becomes equal to its boiling temperature. Now at this stage the boiling of the liquid would occur.
Also when atoms or molecules of a liquid are wide enough to spread out enough to change from a liquid phase to gaseous phase, then boiling starts to occur. However the temperature does remain constant during the process of boiling of water, even though the heat is supplied constantly. This is because all heat energy provided is used up to change the state of water vapour. Therefore all the heat energy which is supplied to the liquid is used up to increase the kinetic energy of the particles while the temperature remains constant.

So, the correct answer is Option B.

Note:
The process of boiling brings about a physical change i.e. it causes change in the state of the matter or liquid only, and no chemical alteration of the molecule is caused during this process.